On his Code in PHP site *Sarfraz Ahmed * has a post talking about coding to interfaces, how its done and why he thinks it's an essential part of any application.

One of the nicest things you can add to your programming skills is coding to interface.

One of the nicest things you can add to your programming skills is coding to interface. One of the five principles of S.O.L.I.D is Dependency inversion principle which states: [...] High-level modules should not depend on low-level modules. Both should depend on abstractions [and] abstractions should not depend on details. Details should depend on abstractions.

He elaborates on this "pretty formal definition" with an example MySQL wrapper class used in a User class, making them tightly coupled to each other. He also points out the same with a `UserController. As a solution to this tight coupling problem, he suggests using dependency injection (inversion of control) to pass in instances of the classes rather than creating them internally. This still couples them, though a bit more loosely, so he suggests using an interface for the dependency instead of a concrete class. This way any number of potential classes could be passed in and the class internally knows how to use them.

The Laravel News site has a post today linking to five handy resources you can use to learn about the Laravel IoC (inversion of control, dependency injection) container.

The Laravel IoC container is a powerful tool for managing class dependencies. It is widely used in Laravel and an important tool for your arsenal. The community has created several tutorials for this and here are five resources that will teach you all about it. [...] By reading these tutorials you’ll be up to speed in no time on the Laravel IoC container and also improve your code by implementing it in your application.

As a "bonus" there's also a link to a video narrated by Laravel creator Taylor Otwell himself about the IoC container and its use.

Inversion of Control, or IoC, is a technique that allows control to be inverted when compared to classical procedural code. The most prominent form of IoC is, of course, Dependency Injection, or DI. Laravel's IoC container is one of the most used Laravel features, yet is probably the least understood.

He starts with an example of basic dependency injection (constructor injection) and how this relates to the Laravel framework's IoC handling (hint: it's all IoC). He includes examples of some built-in Laravel bindings and talks about the difference between shared and non-shared bindings. He also looks at conditional binding, how dependencies are resolved and how you can define your own custom binding implementations. Other topics mentioned include tagging, rebounds, rebinding and extending. He ends the article with a look at how you can use the IoC outside of Laravel too.

The SitePoint PHP blog has a new tutorial posted showing you how to use the Laravel dependency injection container to handle dependencies in you Laravel-based applications. Younes Rafie introduces some of the basic concepts behind dependency injection and the various types to get everyone started on the same level.

As developers, we are always trying to find new ways to write well designed and clean code by adopting new styles, using design patterns, and trying new robust frameworks. In this article we will explore the dependency injection design pattern through Laravel’s IoC component and see how it can improve our design.

He includes examples of the three basic types of injection - controller, setter and interface - with brief code examples of their implementation. He goes on to talk about the "Inversion of Control" principle (part of the SOLID set of principles) and how the Laravel dependency injection container helps by binding objects and instances for later retrieval. Code examples for session storage handling (through a MySQL database) are included that are automatically resolved as the class requires them.

In Zend Framework 1, it was difficult to follow best practices when it came to writing testable code. Sure, you could make testable models, but once you need those models in a controller, what do you do? Zend Framework 2 makes it much easier. In this post, I'll cover the basics of injecting a model into a controller. The main goal here is to be able to wire up and configure your application from the highest level possible. Constructor injection + inversion of control makes it easy to determine which classes are dependent on other classes.

He creates a "Building" module and a "BuildingController" inside of it. This controller takes in an instance of a "Building" model as a dependency. He also shows how to define this dependency in the "getControllerConfig" method of your module to make it work automatically. He makes the "Building" model itself with no dependencies and sets it up as an "invokable" in that same "getControllerConfig" method.